Cleaning of CHF₃ plasma-etched SiO₂/SiN/Cu via structures with dilute hydrofluoric acid solutions

After etching in a CHF₃/Ar electron cyclotron resonance plasma, SiO₂/SiN/Cu via structures for multilevel Cu interconnection were investigated with angle-resolved x-ray photoelectron spectroscopy. Photoelectron shadowing, determined by x-ray photoelectron spectroscopy takeoff angle, and electrostatic charging were used to determine the chemical composition and amount of contamination on the dielectric horizontal surfaces and via sidewalls, as well as on the Cu at the bottoms of the via holes. All surfaces were covered with one to two monolayers of a CF_x layer (CF > CF₂ > CF₃). The dielectric surfaces were also covered with a small amount (∼0.1 monolayers) of Cu, and the Cu at the bottom of the via was contaminated with O (mainly CuO) and F. After cleaning with dilute HF solution, the dielectric surfaces were free of Cu and most of the F and C. CuO was also removed from the Cu surface by this treatment; however, Cu₂O and CF_x remained.